\begin{tikzpicture}
  \matrix (m) [minst]
  { 
    \node (m-1-1) [instr]{}; & \node (m-1-2) {}; \\
    \node (m-2-1) {};        & \node (m-2-2) {}; \\
    \node (m-3-1) {};        & \node (m-3-2) [instr]{$i_1$}; \\
    \node (m-4-1) {};        & \node (m-4-2) {}; \\
    \node (m-5-1) {};        & \node (m-5-2) [instr] {$i_2$}; \\
    \node (m-6-1) {};        & \node (m-6-2) {}; \\
    \node (m-7-1) {};        & \node (m-7-2) [instr] {\verb|return|}; \\
    \node (m-8-1) {};        & \node (m-8-2) {}; \\
    \node (m-9-1) [instr]{}; & \node (m-9-2) {}; \\ 
};
\draw (m-1-1) |- (m-2-2);
\draw (m-2-1) -| (m-3-2);
\draw (m-7-2) |- (m-8-1);
\draw (m-8-2) -| (m-9-1);
  \path[-stealth]
    (m-2-1) --  node [above] {$\sigma$} (m-2-2)
    (m-2-2) edge (m-3-2)
    (m-3-2) edge (m-5-2)
    (m-5-2) edge (m-7-2)
    (m-8-2) --  node [above] {$\tau$} (m-8-1)
    (m-8-1) edge (m-9-1);
\end{tikzpicture}
